1. Field of the Invention
The present invention relates to an audio signal processing circuit.
2. Description of the Related Art
Recently, an FM (frequency modulation) transmitter circuit is used to reproduce music data recorded in a portable music reproduction device or the like, by a car stereo, for example (See Japanese Patent Laid-Open Publication No. 2007-88657, for example.)
FIG. 6 is an example of a configuration of a transmission device 200 for transmitting an audio signal. When an audio signal from a portable music reproduction device (hereinafter referred to as “a music reproduction device”) 210 is reproduced by a car stereo (not shown,) a user first operates a setting device 310 for starting an FM transmitter circuit 300. A microcomputer 320 outputs to the FM transmitter circuit 300 a control signal for starting the FM transmitter circuit 300 based on an operation result of the setting device 310. The user then take into consideration a frequency of an FM radio or the like being used in a surrounding area, and operates the setting device 310 so as to set a transmit frequency of the FM transmitter circuit 300. The microcomputer 320 outputs data corresponding to a desired transmit frequency to the FM transmitter circuit 300 based on the operation result of the setting device 310. Thereafter, when the user reproduces music stored in the music reproduction device 210, a carrier wave set in the FM transmitter circuit 300 is frequency-modulated by the audio signal, to be transmitted to the car stereo.
On the other hand, in order to stop reproduction of music performed by the car stereo, the user operates the music reproduction device 210 so as to stop output of the audio signal. Then, the user stops the FM transmitter circuit 300, that is, operates the setting device 310 so that there is no power consumption in the FM transmitter circuit 300. As a result, the microcomputer 320 outputs to the FM transmitter circuit 300 a control signal for stopping the FM transmitter circuit 300. As mentioned above, the user operates the music reproduction device 210 and the setting device 310, to be able to reproduce by the car stereo music stored in the music reproduction device 210 and stop reproduce it.
In order to start or stop the above-mentioned FM transmitter circuit 300, the microcomputer 320 needs to output a control signal for starting or stopping the FM transmitter circuit 300 based on an operation result of the setting device 310. That is, in the transmission device 200, a circuit for controlling the FM transmitter circuit 300, such as the microcomputer 320, should generate a control signal for controlling a state of the FM transmitter circuit 300.